How to build The Foundation and Platform for a Treehouse

The Treehouse Foundation

They say the most important thing to building anything is it's foundation. Others may argue it is location, location, location. I discovered I had both. If you missed Part 1 of The Treehouse Project click here to read where the inspiration was born.

After I finish building the treehouse I will post a video to my YouTube Channel. You can subscribe to it by clicking the below subscribe button. I post a lot of DIY videos and showcase the projects that I work on around my house.

Threehouse location

Post hole that is 8in diameter and 3ft deep

8in diameter Concrete footing with bolt and base plate

I made sure my foundation was solid. I used my brother-in-laws gas auger to dig 3 feet down into the hard clay. I then mixed about 2.5 bags of concrete for each hole. Next I attached a concrete anchor bolt and base plate. This plate is what holds the 4x6 post. It took some time to dig all the holes and attach the base plates. One base plate gave me some issues as the bolt didn't secure properly inside the concrete and every time I tightened it, it drew upward. It eventually stopped but I had to hacksaw part of the access bold off because I couldn't put the base plate over it.

This was my first time ever pouring footings and installing anchor bolts and I have to say it was fun and not as hard as I thought it would be. The only real thing you need to keep in mind is to make sure that you purchase the right diameter bolt and nut and the rest is rather easy.

The Posts and Rim Joists

I used four 4x6x10 posts and 2x12 rim joists to build the frame of the platform. After building the rim of the platform I realized I didn't need 2x12, I could have used 2x10. This would have kept costs down and made managing the lumber much easier.

I originally designed the size of the platform to be 14x12 but when I installed the four posts and the rim joists my wife and I looked at it and said it was too big. I have to say I did get a little out of hand with the size of the Treehouse and I agreed that it was a bit too big. My wife and I agreed to make it smaller, so it is now 10x12. I am so thankful for my wife, she helps keep me grounded as I can tend to get caught up in what I am doing. She is my voice of reason and my amazing interior designer. I don't know what I would do without her!

Top photo is the original length and size the bottom is the edited version

Braces for the Stilts to the Treehouse

The hardest part about the construction of the Treehouse so far is my base. This part of the project required help from a good friend of mine, Marc. When you are building off stilts it is very important to keep everything level. This sounds easy but is especially hard when everything is moving around on you. To help with this issue I would recommend using braces.

Once you have your main support posts or stilts braced you can add your outside rim joists. We used a 2x4 block to help hold up the outer rim joist. I then put 2 temporary screws in to hold it in-place. Once it was level and where it needed to be I then drilled two 5/8 holes into each post.

Rim Joists and Stilts

After I drilled the holes I put in a 1/2 galvanized carriage bolt. I had to end up using two different lengths, 6in and 8in, for the 4x6 post

Carriage bolt in 2x12

tightening the blot with my socket wrench

Next I used my socket wrench to tighten the bolt carriage blot. For some reason I really enjoyed this part of the build process. I think it was because I could see it all coming together and it reminded me of the old erector sets you played with as a kid.

The Platform

To build a proper platform you need to have joists. I put my joists 16in apart from each other and used joist hangers. Adding joists also stiffened up the platform and made it less wobbly.

2x10 Joists

Next I added the floor boards. I used 1in floor boards that were 16ft long. I then used 1 5/8 deck screws. Yeah, I have no shoes on - this was on purpose to bring me back to my childhood. See, I rarely wore shoes as a kid. I would build most of my Treehouse and forts without shoes. You can read my back story here. So far this was my favorite part of the build. I could smell the lumber and feel the wind blowing in the evening breeze. I stayed out there till the sun went down and I could no longer work, and it was wonderful.

Screwing in the deck screws

The next morning my daughter wanted to see the platform. I took her outside and carried her up the ladder. She was so, so excited. She had a million questions, "Where is her house, where is her bed, where is the water cannon etc." She asked me why the deck was hanging off, I told her that I did that so I could trim it, and the rest of the Treehouse was still under construction. She believed that to be an acceptable answer.

Stay tuned my next blog post will feature the framing of the clubhouse.

If you have any comments or questions please feel free to leave me a message.